I'm hoping that people actually having to know/find their language code is a bit of a short-term anomaly. As new projects come out, I hope they'll just mux in these tracks with the correct language code and then nobody will need to download Project Threepio as a separate package. They'll just play the video and their player will display the full language names in the subtitles menu.

This is ultimately designed as a supply-side project, even though the SUP files have yet to actually be used in a preservation--and the language codes can be helpful for disc authors (keeping the filenames as short as possible can be a virtue with certain authoring software), as well as for many of the utilities I use for creating the subtitles in the first place, so they're staying as-is.